As to High-Speed Downlink Packet Access (HSDPA), user equipment (UE) reports the measured channel quality of High-Speed Downlink Shared Channel (HS-PDSCH) to the Media Access Control-high speed (MAC-hs) functional entity of node B. According to the reported channel quality, the MAC-hs functional entity selects the next data transmission format (e.g. the size of data blocks, modulation format, the number of HS-PDSCH channel codes, etc.) and performs the downlink channel power control.
The period the UE reporting the channel quality is determined by Radio Network Controller (RNC). In general, the period is 1-80 HSDPA Transmission Time Intervals (TTI), one HSDPA TTI is 2 ms. However, due to transmitting and processing delay, the channel quality the MAC-hs receives is not the real reflection of the current downlink channel quality, seeing as the downlink channel often undergoes changes caused by fading, hindering, interfering and the like. In particular, when the period for reporting the channel quality is relatively long, if the MAC-hs directly employs the channel quality reported by the UE to perform user scheduling, data transmission format selecting and power controlling, then resources of the system cannot be utilized fully and effectively.
In order to enable the MAC-hs to track channel changes in real time to implement link adaptation better, it can be considered using Fast Power Control (TPC) information to interpolate channel quality, since the uplink Dedicated Control Channel (DPCCH) uploads the TPC information per time slot. Generally, the interval between time slots is ⅔ ms, and the TPC information usually reflects the changing trend of adjacent time slots of downlink channel.
In some cases (for instance, the bad uplink Dedicated Control Channel quality results in TPC decoding errors; the fact that inner loop power control fails to keep the track when UE is moving at a high speed, leads to errors in TPC; and UE is in a soft-handoff state), however, the TPC information is not correlated with the change trends of the downlink channel HS-PDSCH. If the interpolating using TPC information is still employed to obtain channel quality, then negative effects will be produced, let alone benefits.
The document “TSG R1#17 (00) 1378” disclosed during the meeting “TSG-RAN Working Group 1 meeting #17, Stockholm, Sweden, Nov. 21-24, 2000” proposed a method of obtaining real-time channel quality by interpolating using fast power control information TPC and downlink channel signal noise rate SNR reported by UE, which is incorporated into the present invention by reference.
However, the document “TSG R1 # 19 (01) 0231” disclosed during the meeting “TSG-RAN Working Group 1 meeting #19, Las Vegas, Nev., USA, Feb. 27-Mar. 2, 2001” pointed out that the aforesaid method of obtaining real-time channel quality by interpolating using fast power control information TPC and downlink channel SNR reported by UE cannot achieve good results during soft handoff and hence, suggested stopping interpolating at that time. Since only RNC knows whether the UE is in the soft-handoff state, whether or not to interpolate channel quality rests upon the RNC's notification. This leads to signaling overhead between node B and RNC, and needs to modify the existing protocols. The aforesaid document is incorporated into the present invention by reference.
Therefore there is a need for a method capable of carrying out reliable channel quality interpolating.